The gut microbiota plays an important role in several diseases, as gut microbiota lies at the interface with the gut, the host immune system and the environment. A typical human gut microbiota comprises thousands of microbial species, among which commensal, beneficial or pathogenic bacteria. The role of each of these microorganisms is hardly described; however it is known they change their behavior in diseased individuals in favor of the pathogenic potential of certain commensal bacteria. The microbial content of the gut is believed to weigh about 1.5 kg and to outnumber the cells of the host by 10 to 1. Inflammatory bowel diseases are characterized by an aberrant immune response occurring in a genetically predisposed host in response to microbes and/or microbial compounds found in the gut microbiota.
Crohn's disease (CD) is a chronic inflammatory bowel disease (IBD) that may affect any part of the gastrointestinal tract from mouth to anus. The age of onset is generally between 15-30 years and it is equally prevalent in women and men. The highest prevalence is found in Europe and North America with just over 300 per 100.000 persons (Molodecky et al. 2012). CD generally leads to abdominal pain, severe diarrhea and weight disorders. The disease is of unknown aetiology and multifactorial: environmental factors, host genetics and gut microbiome have all been shown to impact the risk of disease and its severity (Cho et al (2011)). The clinical diagnosis of CD is supported by serologic, radiologic, endoscopic, and histologic findings.
Ulcerative colitis (or UC) is another form of inflammatory bowel disease (IBD). Ulcerative colitis is a form of colitis, a disease of the colon (the largest portion of the large intestine), that includes characteristic ulcers, or open sores. The main symptom of active disease is usually constant diarrhea mixed with blood, of gradual onset. Ulcerative colitis has the same etiology as CD, but CD can affect the whole gastrointestinal tract while UC only attacks the large intestine.
Of the bacteria that may play a role in the pathogenesis of these diseases, a pathotype of E. coli, called “AIEC” for “adherent-invasive Escherichia coli”, has been strongly implicated (see in particular Boudeau et al., 1999). AIEC are able to adhere to the intestinal epithelium and colonize gut mucosa where they participate to IBD onset. More precisely, AIEC were found to be associated with ileal mucosa in 36.4% of CD patients compared with 6.2% of controls, suggesting that these bacteria are involved in CD pathogenesis (Darfeuille-Michaud et al., 2004).
AIEC are distinct from other pathogenic intestinal E. coli strains because they do not harbor genes typically associated with pathogens such as enterotoxigenic, enterohemorrhagic, enteroinvasive, enteroaggregative, and enteropathogenic E. coli (Boudeau J et al, 1999).
AIEC's adhesion to mucosal epithelial cells is mediated by proteinaceous, rod-like organelles that are called type-1 fimbriae. Type-1 fimbriae carry an adhesin at the edge of a flexible tip fibrillum. This adhesin, FimH, is a lectin having a strong affinity for highly mannosylated glycoproteins (Bouckaert J et al, 2006).
Via FimH, AIEC bacteria adhere specifically to the carcinoembryonic antigen-related cell adhesion molecule 6 (CEACAM6), a mannosylated glycoprotein which is abnormally expressed in the ileal mucosa of 35% of CD patients (Barnich N et al, 2007). Overexpression of these CEACAM6 molecules in CD patients, acting as receptors for E. coli adhesion in the gut, favors ileal and colonic AIEC invasion and their intracellular survival and replication within the mucosal tissues, thereby amplifying immune responses in IBD patients.
Moreover, it has been shown that point and pathoadaptative mutations in the FimH adhesin confer significantly higher ability to adhere to CEACAM-expressing intestinal epithelial cells, thus leading to an abnormal colonization of the gut and to the development of chronic inflammation in a host (Dreux et al, 2013).
AIECs have also been demonstrated to be implicated in inflammatory bowel diseases of animals such as dogs and cats, in particular in connection with animals suffering from CD or from granulomatous colitis (also called histiocytic ulcerative colitis), a disease close to the corresponding human ulcerative colitis (Bronowski et al, 2008; Martinez-Medina et al, 2011; Mansfield et al, 2009 and Martinez-Medina et al, 2014).
As patients suffering from an inflammatory bowel disease have a five-fold increased risk of developing colorectal cancer (CRC), AIECs are strongly suspected to be involved in the pathogenesis of CRC. Already, E. coli strains with similar features to AIECs, and belonging to the B2 and D phylogenetic groups, have been associated with CRC, in particular E. coli strains exhibiting adhesion properties to the ileal and colonic mucosa (Martin et al, 2004; Raisch et al, 2014; and Bonnet et al., 2014).
Such Adherent E. coli (AEC) have also been demonstrated to be involved in auto-immune inflammatory diseases such as celiac disease. In particular, AIECs are suspected to play an important role in the onset of celiac disease (Martinez-Medina et al 2, 2014).
AEC are also suspected to be involved in inflammatory bowel syndrome (Sobieszczanska et al, 2012), and in metabolic diseases such as metabolic syndrome, obesity, diabetes (type 1 or 2), hypercholesterolemia (see in particular Martinez-Medina et al 1, 2014).
Finally, extraintestinal E. coli strains largely sharing characteristic features of AIECs have been found to cause urinary tract infections (UTIs). These E. coli strains, called UPECs (UroPathogenic E. coli), specifically bind to uroplakin 1a on the bladder epithelium, which results in bacteria invasion of the bladder mucosa, via phenomena similar to those described in case of ileal and colonic AIEC invasion (Chen et al, 2009; Bronowski et al, 2008).
As AIECs, UPECs and AECs invasiveness, anti-phagocytic and pro-inflammatory properties have been demonstrated to be involved in UTIs and are likely to be involved in IBD (in humans as well as in animals), IBS, CRC and auto-immune diseases (such as celiac disease) onset, this is of crucial importance to elaborate a strategy to eradicate these different bacteria from the digestive and/or urinary tract.
A promising strategy to prevent and treat the above pathologies would be to inhibit the adhesion of AIECs, UPECs and AECs to the epithelial cells of the digestive and/or urinary tract mucosa.
To date, heptylmannose (HM) is still one of the most efficient FimH antagonists and a potent in vitro AIEC and UPEC adhesion inhibitor (Bouckaert et al, 2005, Bouckaert et al, 2013). HM is generally used as a reference in the antiadhesive assays but proved disappointing in vivo. Indeed, millimolar concentrations are required to observe a significant bacterial load reduction in a cystitis murine model (Wellens et al, 2008) and gave no effect with AIEC in a CEABAC 10 Crohn's disease model.
To improve the therapeutic effect of HM, WO 2014/016361 proposed in particular mannose derivatives of formula (IV) and (IV′), which all possess a heteroatom (NH) link between the anomeric carbon of the mannose moiety and the aromatic aglycon. A hydrocarbon link was not envisaged as it was expected to change the overall conformation of the mannose moiety (a 1C4 chair conformation is indeed expected in such derivatives, see Schwardt et al, 2011), thus preventing the required interactions to occur between the FimH adhesin and the mannose moiety of the carbon analogs of the compounds of formula (IV) and (IV′) of WO 2014/016361, resulting in a lower affinity of the compounds. Additionally, the crystallographic structure of a compound of formula IV in the FimH binding site showed a stabilizing hydrogen bond between the anomeric NH and a water molecule (Brument et al, 2013). This interaction is precluded when switching the NH group for a CH2.
Surprisingly however, the present inventors discovered that mannose derivatives with a hydrocarbon link between the anomeric carbon of the mannose moiety and the aglycon proved very efficient in inhibiting the interaction between FimH and its receptor (CEACAM6 in the intestine or uroplakin 1a in urinary tract). Said compounds proved also stable under acidic conditions comparable to the ones encountered in the stomach, and are little or not sensitive to hydrolysis by glycosidases, in particular intestinal glycosidases, two properties required for further clinical developments.